The present invention relates generally to systems, methods and apparatuses for producing fertilizer and/or mixed fuels. More particularly, the invention relates to systems, methods and apparatuses that use stranded natural gas as a feedstock to produce high nitrogen fertilizers such as urea.
The market for high nitrogen fertilizers such as urea (which contains about 46% nitrogen) continues to grow. For example, U.S. domestic consumption of urea has experienced a 1.2% growth rate per year for the past six years. In 2008, North American consumption exceeded 6.5 million tons while domestic production was less than 4.5 million tons. Consequently, the balance had to be supplemented with imported product.
The growth in demand for urea stems from its versatility, portability, and capability. Urea has various uses, including use as an agricultural fertilizer, as raw material input for production of plastics, and use by the surfactant industry. Moreover, urea is compatible with the local and regional markets for the product. Further, urea is also beneficial due to manufacturing cost per ton of production. Additionally, urea has a number of advantages over other nitrogen fertilizers. For example, urea is safer to ship and handle and is less corrosive to equipment. It also has a higher analysis than any other dry nitrogen fertilizer. Furthermore, the high analysis means a reduced transportation and application cost per pound of nitrogen. It can also be applied in many different ways, from sophisticated aerial application equipment to manual hand spreading. Urea is also highly water soluble so it moves readily into the soil. In addition, it can be used on virtually all crops. Another benefit is that the manufacturing of urea releases few pollutants to the environment. Urea can also be stored and distributed through conventional systems.
The advantages of urea relative to other fertilizers helps make urea the major fertilizer traded in international commerce. In the very near future, urea is expected to account for more than 50% of the nitrogen fertilizer in world trade. When compared to other dry fertilizers, urea has captured more than 65% of the world fertilizer trade.
Currently, over 90% of the urea produced utilizes natural gas as the feedstock. Over the past several years, natural gas costs have risen dramatically. In some cases, a 50% increase has been realized. During the winter of 2000-01, natural gas prices experienced a 400% increase. Because of natural gas prices, U.S. domestic nitrogen fertilizer production has dropped and imports have risen.
Urea production is natural-gas intensive. To produce one ton of nitrogen fertilizer from natural gas requires the consumption of between 20,000 and 33,800 cubic feet of natural gas. Utilizing 33,800 cubic feet per ton as an example, and considering each cubic foot of natural gas contains 1031 BTU's; one ton of fertilizer made from natural gas contains the equivalent of over 34.8 million total BTU's. In terms of gasoline equivalents, this would amount to over 300 gallons of gasoline per ton of fertilizer produced. Therefore, producing urea from normal sources of natural gas (i.e., non-stranded sources) is a costly proposition.
The use of stranded or flared natural gas sources, which are economically unviable for oil producers, could become a viable source of feedstock for urea production only if the quality of the incoming gas stream could be controlled and a low cost small production facility could be made available which does not require the high BTU content of the typical natural gas stream. Current global natural gas reserves total approximately 6,100 trillion cubic feet (tcf), according to U.S. Energy Administration Information estimates. Of these, roughly half are considered to be “stranded,” that is, uneconomical to deliver to market. In addition, the World Bank estimates that over 150 billion cubic meters (bcm) of stranded natural gas are flared annually. When dealing with stranded natural gas, oil producers often find the energy, or BTU content, is too low; the gas is too impure to use; or, the volume is too small to warrant a pipeline connection to the gas infrastructure. In addition, the stranded gas is sometimes produced along with the oil, becoming an environmental liability. This unwanted, non-commercial by-product of oil production has become a major problem in oil fields where producers have been forced to abandon well sites early, leaving valuable reserves of domestic oil untapped.
Typically, there are three ways to deal with stranded gas: (1) venting or flaring the gas, which contributes to air pollution without any beneficial offsets from the gas; (2) using electrical energy to re-inject the gas, which incurs significant extra costs; and (3) shutting down oil production, which leaves valuable oil in the ground.
Another form of stranded natural gas is “associated gas,” or gas found in association with development of large oil fields. While crude oil can be transported to distant markets with relative ease, the practice in the past has been to flare associated gas at the wellhead. This practice however is no longer acceptable due to environmental concerns and, more recently, due to the growing economic value of these reserves in a high-energy price environment. Oil producers are now looking to use technology to capture associated gas (stranded gas) and take it to consuming markets.